Page 312 - IJB-9-4

International Journal of Bioprinting Biomechanical properties of 3D printable material

mimic the biomechanical properties of a human aorta. Table 1. RGD450+TangoPlus material printed with different
These synthetic materials are not biocompatible. Therefore, shore hardness and thicknesses
phantoms were used to carry out the biomechanical study Thickness of RGD450+TangoPlus material (mm)
and simulation. Two groups of materials were tested:
thermoplastic polyurethane and rubber-like materials. 70 SH 2
60 SH 2
2.1.1. Thermoplastic polyurethane 50 SH 2 2.5 3 3.5
Two thermoplastic polyurethane materials, NinjaFlex 40 SH 2.5 3 3.5 4
(Fenner Inc., Manheim, USA) and Filastic (Filastic
TM
Inc., Jardim Paulistano, Brazil) were provided by Dijon
3D Company (Dijon, France). The NinjaFlex material was 2.2. Method
printed at a temperature of 225°C–235°C. Heating plates The aortic wall sample from a healthy patient was preserved
were not required during printing. The printing speed was in phosphate-buffered saline during the transfer from the
15–35 milliseconds per meter. The MakerBot (MakerBot autopsy room to the laboratory for tensile experiment. Due
Industries, USA) 3D printer equipped with a Thingiverse to the regional differences in biomechanical properties of
[12]
driver block (MakerBot Industries, USA) was dedicated the aortic wall , the samples were cut into smaller square
to NinjaFlex printing. The machine was kept at a strict samples (15 mm × 15 mm) in order to mimic standard equi-
horizontal position during the printing process. In order biaxial experiments on aortic tissue. The average thickness
to minimize printing errors (within 0.05 mm), the 3D was measured using an electronic micrometer (Litematic
printing machine was adjusted by a standard scale. The VL-50, Mitutoyo®, Japan) before loading. Each aortic
diameter of the original material was 1.75 mm, with 85 specimen was labeled according to their circumferential
shore hardness (SH). For experimental purposes, different and longitudinal directions with respect to the blood flow
thicknesses of NinjaFlex material were printed, ranging in the aorta. Biomechanical experiments were carried out
from 0.2 mm to 1.8 mm in 15 mm × 15 mm squares. Due using a biaxial tensile test machine (LM1 Planar Biaxial,
to printing process issues and low thickness managements, TA Instruments, USA, Figure 3). The preconditioning was
samples ranging in thickness from 0.2 mm to 0.7 mm were set to 10% of the experimental sample length (10 mm),
excluded in this study. Phantoms from the second material, with 10 loading-unloading repetitions.
the 85-SH Filastic , were printed at a nozzle temperature Only uniaxial tests were performed on the thermoplastic
TM
of 220°C–240°C. A heating plate was necessary for polyurethane material due to its isotropic behavior during
printing, and the heating stability should be 100°C–110°C. the printing process, whereas biaxial tensile tests were
During the printing process, the distance between the gear performed on the healthy human aorta and the rubber-like
and the printing tube was controlled to be constantly less material. All tensile tests were repeatedly performed, and
than 5 mm. The thickness interval of the material could surgical hooks were used to secure the connection between
only be controlled within 0.05 mm due to the material’s the sample and the system. Only one result per material
characteristics. Different thicknesses of Filastic were per thickness was preserved in our study: the one with the
TM
printed, ranging from 0.5 mm to 0.85 mm in 40 mm × smoothest stress–strain curve.
40 mm squares.
The maximum Young’s modulus, also known as the
2.1.2. Rubber-like material (RGD450+TangoPlus) elastic modulus, was calculated for the evaluation of sample
RGD450+TangoPlus is an advanced rubber-like material stiffness . The printed material was studied according to
[25]
that can be printed with a smooth surface by ENNOIA three parameters: thickness, the maximum value of Young’s
Company (Besançon, France) using the Connex3 modulus, and the stress–strain curves.
TM
Object500 3D printer (Stratasys Ltd. , Israel). It is a
©
composite material of RGD450 and TangoPlus (Stratasys 3. Result
Ltd. , Israel). Materials of different shore hardness were 3.1. Thickness and maximum Young’s modulus
©
printed and tested (Table 1). Although the size of the There was a difference between the expected printed
printed RGD450+TangoPlus specimens was 40 mm × thickness and the experimentally measured thickness
40 mm, the size of the tested RGD450+TangoPlus (Tables 3 and 4). Nevertheless, the maximum Young’s
specimens was only 15 mm × 15 mm. Figure 2 shows modulus was compared among materials.
the printed RGD450+TangoPlus specimens. The tested
specimens maintained directional consistency during 3.1.1. Human aorta
testing. The direction was fixed according to the biaxial test The aortic wall had a mean thickness of 1.49 ± 0.34 mm.
system and was defined as A and B. The mean failure stress and maximum Young’s modulus

Volume 9 Issue 4 (2023) 304 https://doi.org/10.18063/ijb.736